Additive manufacturing enables producing shapes that would otherwise be expensive, or impossible to achieve. Stereolithography, specifically, offers highest resolution as it is primarily limited by the optical exposure system. With Hot Lithography, it is now possible to produce precise parts with industrially relevant material properties. We show resolution capabilities of laser scanning over an area of 200 mm x 100 mm, utilizing polymerization triggered by single photon absorption, and its applications in fields traditionally relying on microfabrication technologies. We elaborate, how Hot Lithography provides technological and economic opportunities in areas such as the electronics industry, fluidics, and medical devices.
Fast laser curing is essential for highly accurate, high throughput additive manufacturing. High performance resins however exhibit relatively slow curing kinetics. In this talk we elaborate on the question if photopolymers relevant for technological applications can be processed with high-speed laser scanners. This is necessary to develop 3D printing systems that can compete in terms of accuracy and throughput with traditional manufacturing methods but outperform in terms of freedom of design and design agility. We compare exposure times spanning nine orders of magnitude and assess curing depths and double bond conversions obtained with different energy dosages and power densities.
For additive manufacturing, scanning systems based on diode lasers offer unique advantages over conventionally used solid state lasers. Their fast modulation and high beam quality allow the production of precise polymer parts. However, the material portfolio which conventionally can be used on such stereolithography (SLA) systems is limited to resins which can be processed at room temperature. By controlled heating of a thinly coated material film (Hot Lithography), the available process window is significantly expanded. We present photopolymers with safe fire behavior of walls as thin as 0.45 mm. Using the precision of diode lasers without sacrificing fabrication speed, these materials are particularly suitable for the production of connectors for electronics industry.
Additive manufacturing of polymer parts via photpolymerization has emerged as versatile production technology. Toolless fabrication of arbitrarily shaped 3D printed parts has shown promise for industrial application, especially when processing high viscosity resins which lead to polymers with enhanced thermomechanical properties. However, until recently these production machines were limited by both field of view and light sources capable of providing sufficient energy density. With the advent of scrolling DLP projectors, high throughput systems could be conceived. By precise signal control and image plane matching, a novel additive manufacturing platform was developed. A pixel pitch of 50 µm is maintained over a printbed of up to 1 m x 0.28 m. It is capable of processing high viscosity resins at a throughput rate increased by over a magnitude compared to conventional Hot Lithography printers, enabling industrial scale production of high performance polymer parts.
In recent years, two-photon polymerization (2PP) has emerged as a promising technology to structure customized biomaterials in regenerative medicine. Based on nonlinear absorption phenomena, 2PP allows rapid and flexible fabrication of fully three dimensional (3D) objects with sub-100-nm resolution.
The ever-growing need for biocompatible photoinitiators (PI) necessitates knowledge of the spectral two-photon absorption (2PA) characteristics. Matching the laser wavelength to the peak of the 2PA spectrum of a particular compound can result in a significant increase of the PI’s performance. With the advent of tunable femtosecond laser systems the application window of 2PP has vastly expanded due to the broad spectral range available for structuring.
To reveal the potential of a certain PI design the z-scan technique has become a standard method to measure the non-linear properties. We have developed a completely automated z-scan setup, which requires negligible user input for the characterization. It is based on the same system used for 2PP, which allows direct comparison of the PI absorption and the polymerisation performance.
To ensure reproducibility and accuracy of measurements, our group developed an automated algorithm, which collects the required laser parameters before the scanning process. These are stored in a comprehensive library for every single measurement. Therefore, even large amounts of data are easily handled and correctly evaluated without the need to manually check each measurement.
Our setup allowed us to reliably determine the absorption properties of newly synthesized PIs and adjust the structuring wavelength. The change in wavelength resulted in significant improvement of the structuring process.
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